Bleaching or decolorizing of clay or other minerals



I Patented Oct. 7, 1930 UNIT D STATES THOM S WEBSTER PARKER, '01 rLmr'roN, ENGLAND, ASSIGNOR 5110 THE DARTMOOR C'EINA CLAY COMPANY, LIMITED, or PLYMPTON, ENGLAND No Drawing. Application filed February 25, 1928, Serial No. 257,108, and in Great Britain February This invention relates to the bleaching or decolorizing of clay or other mineralscontaining in their naturalstate iron compounds adapted to be partially removed by treatment with an acid. g

It has been found that in bleaching or de-' colorizing clay and other minerals of the character in question by the use of acid alone or in conjunction With a reducing agent and subsequent washing, the reduction of the iron content ot the material to a degree which will render the samefsuitable for a variety of industrial purposes is impossible; for instance, v

by treating a sample of china clay containingv 0.13 per cent. of ferric oxide with acidanda reducing agent, filtering and washing with Water, the bleached suspension containing 28.6 per cent. of clay and 0.65per cent. of sulphurous acid, only 82 per cent, of the iron washing with water did not reduce the iron content ofthe clay.

The present invention is based upon the observation that by the employment of solua tions of soluble. salts (polyvalent' metals yielding colorless compounds with acidic radicles which are non-chromophoric and of which the acid radicles do not form insoluble iron compounds) in the washing of the association with the clay or other mineral as well as in the water used for washing the bleached clay or other mineral.

Thepresence of the salt in the bleaching liquid and in the water used for washing may BLEACHING OR DECOLORIZING OF CLAY OBI. OTHER MINERALS or by securing the formation of the desired salt in the liquid or water, for instance by .of the invention.

was separated from the clay and further clay subsequent to its having been treated with an acid alone or in association with a bleaching agent the removal of iron from the ATENT OFFICE besecured by introducing the salt as such into the liquid or the water, as the case may be,

the addition of an oxide, hydroxide or carbonate of a suitable metal orthe metal itself if necessary together with acid to the Water or the liquid.

' As will be understood, salts of metals, the acid radicles of which form insoluble iron compounds, are not suitable for thepurposes The effect of a given molecular proportion of a salt of metal required would appear to depend on the valency of the positive ion;

the higher the valency of the ion the smaller the proportion of the salt or other compound required to ensure a particular degree of removal of iron from the clay.

As above indicated, generally speaking, the

presence of aluminium salts in the liquid or washing water is to be preferred and sulphate A of alumina, for instance alumina-ferric or potassium, sodium or ammonium alums may be conveniently employed.

The following particulars are given by way of example to illustrate suitable methods of carrying the invention into effect and the results achieved in particular cases.

E wample I 7 China clay containing 0.133 per cent. of ferric oxide as coloring matter is bleached in the form of a suspension containing 28.6 per cent. of clay and 0.65 per cent. of sulphurous acid. The suspension is then filtered and the clay washed on the filter at first with a 0.9

per cent. solution of potassium alum and then with water to which no alum had been added,

the weight of potassium alum solution used being 40 per cent. of the .dry weight of the clay and the weight of the Wash water subsequently used being per cent. of the dry weight of the clay. In this way 99.5 per cent. of the iron present as coloring matter was separated from the .particular clay treated.

Example I I .per cent. ofclay, 0.17 per cent. of sulphurous acid and 0.13 per cent. of commercial 14 per cent. sulphate of alumina. The suspension was filtered and the clay washed with a 1.16 per cent. solution of sulphate of alumina followed by water to which no addition had been made. The weight of sulphate of alumina solution used was 40 per cent. of the dry weight of the clay and the Weight of the wash water was, as in the preceding example, 120 per cent. of the dry weight of the clay. In this manner 96.6'per cent. of the iron present als coloring matter was separated from the c ay. After the extraction of the iron is completed the clay can be substantially neutralized by washing with water alone but if desired neutralization of any acid in the clay may be e'fiec'tedby the addition of alkali, for instancecaustic soda, sodium carbonate or lime, to the wash water. K i Generally speaking, the greater the quan tity of iron in the clay the greater should be thequant-ity'of aluminium or other salt used in washing.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is 1. The process of decolorizing clay and other minerals containing, in their natural state, iron compounds adapted to be partially removed. by treatment with an acid which comprises subjecting the said minerals to the action of an acid decolorizing agent, filtering the material so treated and washing the filter residue wit an aqueous solution of a salt of a polyvalen metal which yields colorless compounds with non-chi'omophoric acid radicles.

2. The process of bleaching clay andother minerals containing, in their natural state, iron compounds adapted to be partially removed by treatment with an acid which com-' prises subjectin the same to the action of a sulphurous" aci' filtering the material so treated and washing the filter residue with an aqueous solution of a salt of a polyvalent metal which yields colorless-compounds with non-chromophoric acid radicles.

3. The process of bleaching clay and other minerals containing, in their natural state, iron compounds adapted to be partially removed by treatment with an acid, which comprises subjecting the said minerals -to the,

action of an acid under reducing conditions, filtering the n'gateri'al and washing the filter residue withasolutioh of an aluminium salt.

4;. The process of bleaching clay and other minerals containing, in their natural state, iron compounds adapted to be partially removed by treatment with an acid, which comprises subjectin thesaid minerals to the action of an -aci under reducing conditions, filtering the material and washing the filter in the form of a suspefision containing 28.6

with an acid which comprises treating the same with an acid reduc ng agent, filtering the material so treated, washing the filter residue with an approximately 1 per cent. aqueous solution of an aluminium salt equivalent to per cent. b of the clay an equivalent to 120 dry weight of the clay- 6. The process of bleaching clay and other in their natural state,- iron compounds adapted to be partially reminerals containing,

weight of the dry weight subsequently with water per cent. by weight of the moved by treatment with an acid, which comprises subjectingthe tion of an acid under tering the material of a polyvalent metal and an acid.

said minerals to the acreducing conditions. filand washing the filter residue .with an aqueous solution of a salt The process of bleaching clay and other minerals containing,

iron compounds adapted to be partially removedbv treatment with an acid,

, which comin their natural state,

prises subjecting the said minerals to the action of an acid under reducing conditions filtering the material and washing the filter residue with an aluminium salt In testimony whereof name to this specification.

THOMAS WEBSTER PARKER.

and an acid.

I have signed my 

